1. Field of the Invention
The present invention belongs to a field of electric contacts and electric connectors, and relates to an electric contact and an electric connector, which are mounted on a printed circuit board by surface mounting.
2. Related Art
An electric contact is known, which is made of sheet of a metal such as copper alloy and comprises a leg, which contacts a conductor of a printed circuit board, and a connecting part, which is connected to the counterpart electric contact. This electric contact is surface-mounted on the printed circuit board by soldering the leg of the electric contact on the printed circuit board. An electric connector is also known, which comprises such an electric contact and an insulating housing, which holds the electric contact.
When the above-mentioned conventional electric contact is to be mounted on a printed circuit board by soldering, molten solder will be applied to its leg. However, it may be difficult or impossible to solder the electric contact if, for example, another part is mounted too close to the electric contact. When the electric contact is held in an insulating housing to make an electric connector, the insulating housing may interfere and make it difficult to solder the electric contact onto a printed circuit board. Moreover, this work of applying solder requires careful solder quality control, temperature control and the like, and the man-hours required for control are increased correspondingly. Further, if the electric contact is microminiaturized to connect with, for example, a very fine wire (for example, American Wire Gauge size 36 falls in the category of very fine wire, and the diameter of this electric wire is 0.12 mm approximately), the work of applying molten solder to the leg cannot be done by an automatic machine, and it is necessary to do the work manually by a skilled worker. Hence the productivity is low, and this results in an increase in cost.
When an electric connector having a plurality of electric contacts is to be produced, the electric contacts will be produced by sheet metal processing, and these electric contacts will be assembled with an insulating housing or they will be molded integrally. When such production processes are used, the legs of the electric contacts may set irregularly, making it difficult to obtain coplanarity. This, in turn, is likely to lead to defective connection or short circuit. Here the coplanarity means the flatness of the mounting surface when the electric connector is mounted on a printed circuit board or the like.
Now, Japanese Patent unexamined publication gazette Heisei 10-237331 discloses a lead-free ultrahigh-conductive plastic being a conductive resin composite, comprising a thermoplastic resin, a lead-free solder that can be melted in the plasticated thermoplastic resin, and powder of a metal that assists fine dispersion of the lead-free solder in the thermoplastic resin or a mixture of the powder of the metal and short fibers of a metal.
This lead-free ultrahigh-conductive plastic exhibits high conductivity, for example, 10xe2x88x923 xcexa9xc2x7cm or under in volume resistivity. Moreover, this material can be molded by injection molding and has a high degree of freedom in molding. Furthermore, as this material contains solder, there is no need of separately applying solder. One objective of the present invention is to provide an electric contact and an electric connector, which can solve the above-mentioned problems, and a method of connecting the electric contact and electric connector to a printed circuit board by utilizing the lead-free ultrahigh-conductive plastic, which has such excellent conductivity and moldability and contains solder.
To accomplish the above-mentioned objective, an electric contact using resin solder according to the present invention is the electric contact, which is connected to a printed circuit board, which has a conductor being provided on a surface thereof, the electric contact comprises a leg, which contacts the conductor of the printed circuit board, and a connecting part, which is connected to a conductor of a counterpart member, and at least a part of the leg, which contacts the conductor of the printed circuit board, is made of a lead-free ultrahigh-conductive plastic being a conductive resin composite, comprising a thermoplastic resin, a lead-free solder that can be melted in the plasticated thermoplastic resin, and powder of a metal that assists fine dispersion of the lead-free solder in the thermoplastic resin or a mixture of the powder of the metal and short fibers of a metal.
When the leg of this electric contact is made to contact the conductor of the printed circuit board and the leg is heated, the lead-free solder being contained in the lead-free ultrahigh-conductive plastic of the leg will melt out and stick to the conductor of the printed circuit board. When the solder cools and solidifies, the electric contact will be mounted on the printed circuit board. Hence the work of separately applying solder is not required. Accordingly, even when it is difficult or impossible to solder the electric contact, for example, when another part is mounted too close to the electric contact, the electric contact can be mounted on the printed circuit board. Moreover, as solder quality control, temperature control and the like are not required, the control man-hour is reduced correspondingly. Further, even if the electric contact is microminiaturized, the mounting of the electric contact can be done easily by an automatic machine. Hence the productivity is increased and the cost is reduced. The lead-free ultrahigh-conductive plastic exhibits high conductivity, 10xe2x88x923 xcexa9xc2x7cm or under in volume resistivity. Hence the electric resistance of the electric contact can be lowered. Moreover, after the connection of the electric wire, when electricity is passed at a normal level, the lead-free ultrahigh-conductive plastic will not melt out due to heat generation. Further, in comparison with the technology of MID (Molded Interconnection Devices, for example, refer to Registered Utility Model gazette no. 2597015), wherein a conductive plated layer is formed on the surface of an insulator, the lead-free ultrahigh-conductive plastic provides the conductor with a larger cross-sectional area and a larger volume. Hence the resistance of the conductor can be reduced and the heat dissipation is better. This, in turn, allows passage of a larger current. Moreover, as the lead-free ultrahigh-conductive plastic can be molded by injection molding, it gives a greater freedom in molding. Hence it is easy to obtain impedance matching. When the electric contact is formed by injection molding, the accuracy of molding will be improved, and the connector using this electric contact will attain a higher coplanarity than an electric connector using an electric contact of sheet metal. Thus the risks of defective connection and short circuit are reduced. When only a part of the electric contact is made of the lead-free ultrahigh-conductive plastic and other parts are made of a material of which strength and elasticity are higher than those of the lead-free ultrahigh-conductive plastic, for example, a metal, the strength and the elasticity of the electric contact will be enhanced.